Here's another response from Tom... this time, I asked what the viscosity numbers meant. I think I'll just use 0w30 from now on
FROM TOM:
The "0W" part is measured at low temperatures, far below freezing, in fact at -35C for one test and -40C for another. However, in formulating race oils, it can also be looked at as how hard it is for the oil pump to force the fluid through the oil passages and into bearings. Think of sucking a straw stuck in a milkshake vs. milk. Then blow the fluid out the straw. Lot harder with milkshake than milk. Diesel engine oil pumps deliver 10's of gallons per minute and consume 15-20 hp, I think I remember, while gasoline engines are less. But saving 2 or 3 or 4 hp at no cost is always good.
The second number is when the oil is hot, but can loosely be related to how the oil behaves in the bearing. The spinning part, the crank journal or rod journal, is actually surfing over a film of oil and while the 60 psi may seem like what "supports" the moving part, it is not. It only determines whether the oil gets to it's destination or not. The pressure under the theoretical surfboard is 1000's of psi and the oil has to maintain it's film strength to prevent metal contact. So now it has to behave like a thick oil.
Ideally, the W number is as low as you can get it, while the second number is just big enough to keep all the metal parts separated. So 0W-30, 5W-40 are actually very good choices, but because they are made with synthetic base oils (because they can be, and can't so easily be made with mineral oils) they are not very common. Unfortunately, the unfamiliarity of the odd viscosity combination then becomes a barrier to market entry - as you are experiencing - even though it's a really good system.